Electric thermal switch



Feb. 16, 1943. w. H. BULPlT-r 2,311,206

ELECTRIC THERMAL SWITCH -I Filed Nov, s; 1941 INVENTaR HTraRNsY WALTERHeNRv/uLP/Tn Patented Feb. 16, 1943 l ELECTRIC THERMAL SWITCH WalterHenry Bulpitt, Birmingham, England i Application November 3, 1941,Serial No. 417,660 In Great Britain August 1941 (Cl. 'Z4-2) 8 Claims.

This invention relates to electric thermal switches having associatedtherewith a safety device which upon attainment of a ,predeterminedtemperature operates to open the switch, the safety device comprising aratchet wheel normally held against rotation by means of fusible metal,a spring loaded plunger operating in a tube or other support and havinga tooth which co-operates with the ratchet wheel when rthe switch isclosed to hold the plunger against movement under the action of thespring.

The switch may take the form of a plug and socket electric coupling andthe action of moving these coupling members into engagement may operatethe plunger so as to compress the spring and move the tooth of theplunger into engage-Y ment with the ratchet wheel.

One such apparatus is described in my prior speciiication Serial No.229,625 and the present invention is kparticularly applicable to suchapparatus.

The object of the present invention is to con struct the safetyappliance in a manner which allows the parts to be produced andassembled cheaply and to provide means whereby the engagement of theplunger toothy with the ratchet wheel is more positively effected thanhitherto.

According to the present invention in a switch of the kind specified weprovide an inclined guide plate associated with the plunger for guidingits tooth laterally into engagement with the ratchet wheel when theplunger is moved by the closing of the switch.

Further, according to the invention the plunger is provided with aflange remote from the tooth, the ange forming a fulcrum about which theplunger can rock laterally in the tube or support such lateral rockingmotion being produced through endwise movement of the plunger when theswitch is closed by the engagement between the plunger and the guideplate.

The guide plate may have a portion formed as a socket slotted throughone side and end and the plunger, a guide plate and spring can beassembled together as a unit by compressing the spring, passing theshank of the plunger through the slot in the side of the socket portionand then letting the spring expand somewhat to bring the plunger toothinto pressure contact with the end of the socket.

The tube or support in which the plunger is mounted may be provided withan internal shoulder forming an abutment for a portion of the guideplate and the tube or support may further be provided with means toprevent the guide plate from turning about the axis of the plunger sothat the inclined part of the guide plate is retained in the correctposition for guiding the plunger tooth.

The means for preventing the guide plate from turning may consist of agroove in the tube or support into which groove a portion of the guideplate engages.

Referring to the drawing:

Figure 1 is a plan view partly in 'section yshowing one form of theappliance. g

Figure 2 is a sectional plan view taken through the safety appliance.

Figure 3 is a section on line k3--3 Yof Figure 2.

Figure 4 is a perspective view showing the plunger spring and guideplate.'

In the construction illustrated the invention kis shown applied to asafety appliance which co-operates with a plug and socket electricconnector, the socket I0 being mounted in the wall of a vessel IIadapted to be heated by an electric immersion heater I2.

The electric coupling comprises the usual connector I3 having socketsfor engaging with the contact pins I4 carried by an insulating plug I5,this plug being mounted in a metal cap IB having a ange II whichco-operates with the member I0 and packing rings I8 but form a liquidtight joint with the vessel.

The ends I9 of the casing` of the electric heating element are broughtthrough the end of the cap I6 andthe conductors are connected to thepins I4.

The end of the cap I6 is provided with a socket 20 at the centre whichreceives one end of a tube ZI forming the housing for the safetyappliance. The tube 2| is shouldered as shown at 22 and brazed orotherwise secured into the cap I6.

At its opposite end the tube 2I is provided with a circular housing part23 for the ratchet wheel 24 and screwing into the underside of the part23 is a socket 25 which receives the shank 26 of the ratchet wheel 24,the shank 26 being attached to the end ofthe socket by fusible metal 21.

The opening in the tube is shouldered as shown at 28 and it is groovedas shown at 29 from the shoulder to theY end of the bore.

The plunger may be made in two parts, one part 3D having a `flange 3|which is a free t in the tube 2l and the other part forming a shank 32screwing into the part 30 and having a conical head 33 at its end,theconical head having A coil spring 39 is provided operating betweenthe flange 3l and the end of the socket 33.

2. Thermal electric switch of the kind specied having a ratchet wheeland a tube, a plunger mounted for lateral and endwise movement in thetube, a peripheral shoulder on the plunger for engaging a tooth of theratchet wheel, a head on the plunger adjacent said shoulder, an inclinedguide plate in the tube, said guide plate being resilient in a directionwhich is transverse to the length of the plunger, and having a part ofcurved section which partially embraces said head, and means forVlocating the guide plate in vthe tube.

rhe three parts shown in Figure 4 can be l assembled together by placingthe spring on the shank 32, compressing the spring until the toothV 33and the part of the shank adjacent'thereto is exposed, then placing theexposed part of vthe shank through the slot 3l in the socket 35 andallowing the spring to expand somewhat until the shoulder 34 of thetooth 33 comes into con# tact with the end of the socket 36.

The unit thus formed is pushed into the tube ZI until the edge 4i! ofthe socket portion 36 comes into contact with the shoulder 23. When inthis position a part of the spring neck 42 of the guide plate engages inthe groove 29 so that the guide plate is prevented from turning aboutthe axis of the tube ZI.

As seen in Figure 2 the spring 33 is compressed and the shoulder 34 ofthe tooth 33 has been moved laterally by the inclined part 35 of theguide plate into engagement with one of the teeth of the ratchet wheel24.

rIhe safety appliance is moved into this position by the act of engagingthe coupling members I3 and It, the coupling member I3 acting upon theend of the plunger 36.

The end 4I of the tube 2| is brazed lor soldered to the casing of theheating element and preferably to the highest part thereof which rstbecomes uncovered when the liquid in the vessel evaporates. j

Should the temperature of this part of the casing of the heating elementrise above a certain predetermined level the heat will be transmitted tothe end of the tube 2l and thence to the socket 25 and fusible metal 2'1which melts thus releasing the ratchet wheel and allowing it to rotateso as to release the tooth at the end of the plunger. The plunger thenmoves outwardly under the influence of the spring 39 and disengages thecoupling member I3.

The fusible metal 21 will quickly reset so that the ratchet wheel 2dbecomes xed again but the plunger can at any time be pushed inwardly.When the socket I3 is next pushed on to the pins I4 the plunger rockssomewhat about a point on the periphery of the flange 3i when the heador tooth 33 engages with the inclined part 35 of the guide plate andbends back the neck 42 until the shoulder 34 snaps behind one'of theteeth of the ratchet wheel. In this way the head or tooth 33 ispositively guided and forced laterally into engagement with the tooth ofthe ratchet wheel.

What I claim vthen is:

l. Thermal electric `switch of the kind specied having a ratchet wheeland a tube, a plunger mounted for lateral and endwise movement in thetube, a peripheral shoulder onl the plunger for engaging a tooth of theratchet wheel, an inclined guide plate in the tube, said guide platebeing resilient in a direction which isv transverse to the length oi theplunger, and means for locatingthe guide plate in the tube.

3. Thermal electric switch of the kind specified having a vratchet.wheel and a tube, a plunger mounted for lateral and endwise movement inthe tube, a peripheral shoulder on the plunger i for engaging a tooth ofthe ratchet wheel, a head on the plunger adjacent said shoulder, saidhead being of conical form, an inclined guide plate in the tube, saidguide plate being resilient in a direction which is transverse to thelength of the plunger and having a part of curved section whichpartially embraces said head and a resilient neck and means for locating'the-guide plate in the tube. i v

4. Thermal electric switch of the kind specified having a ratchet wheeland a tube, a plunger mounted for lateral and endwise movement in thetube, a peripheral shoulder on the plunger for engaging a tooth of theratchetvwheel, an inclined guide plate in the tube, said guide platecomprising a part adapted to engage the end of the plunger adjacent saidshoulder, a resilient neck, and a socket portion which engages the wallof the tube and means for locating the guide plate in the tube.

5. lThermal electric switch of the kind specified having a ratchet wheeland a tube, a plunger mounted for lateral and endwise movement in thetube, a peripheral shoulder on the plunger for engaging a tooth of theratchet wheel, an inclined guide plate in the tube, said guide platecomprising a part adapted to engage the end of the plunger adjacent saidshoulder, a resilient neck and a socket portion which engages the wallof the tube, said socket portion having a slot extending across its endand along the whole length of one side so that the plunger can beengaged therewith by a lateral motion and means for locating the guideplate in the tube.

6. Thermal electric switch of the kind specified having 'a ratchet`wheel and a tube, a plunger mounted for lateral and endwise movement inthe tube, a` peripheral shoulder on the plunger for engaging a tooth ofthe ratchet wheel, an inclined guide plate inthe tube, said guide platecomprising apart adapted to engage the end of the plunger adjacent saidshoulder, a resilient neck and a socket portion which engages i the wallof the tube, said tube having an internal shoulder forming an abutmentfor locating said socket portion in the tube and a longitudinal slotengaged by said neck portion to prevent the guide plate from turning inthe tube.

'7. Thermal electric switch of the kind specied having a ratchet Wheeland a tube, a plunger mounted for lateral and endwise movement in thetube, a peripheral shoulder on the plungei for engaging a tooth of theratchet wheel, a flange on the plunger remote from said peripheralshoulder, said ange being an easy t in said tube so that the plunger canrock in the tube about said flange as a fulcrum, an inclined guide platein the tube, said guide plate being resilient in a direction which istransverse to the length said guide plate comprising a part adapted toengage the end of the plunger adjacent said. shoulder, a resilient neckand a socket portion which engages the wall of the tube, land means forlocating the guide plate in the tube and a coiled spring on said plungerengaging the end of said socket and said plunger flange.

WALTER HENRY BULPITT.

